1. Field of the Invention
The present invention relates to a flow cell for liquid chromatography of the type in which both the electric conductivity and absorbance of the constituents of a specimen solution dissolved from a column can be measured simultaneously and continuously within the same cell, and more particularly to a flow cell for liquid chromatography which is adapted to measure both the variations with respect to time in electric conductivity and absorbance of a solution flowing at a very low flow rate within the same cell.
2. Description of the Prior Art
Variations in electric conductivity of a solution are one of the factors which exhibit the fundamental properties of an electrolyte and the quantity of the electrolyte can be measured by measuring the electric conductivity of the solution. Furthermore, the variations in volume of a specimen can be measured by measuring the difference in electric conductivities between the solution and specimens contained in the solution.
Furthermore, the properties and the variations in quantity of the constituents of a specimen can be measured by the chemical reactions of particular constituents of the specimen with a light of a predetermined wavelength and by measuring the absorbance of the solution.
These analyzing methods are, for instance, disclosed in the following literatures:
"A Sensitive Low Volume Conductivity Detector for Liquid Chromatography" Robert L. Pecsok et al., ANALYTICAL CHEMISTRY, Vol. 40, No. 11, 1968, Sept., P. 1756-1757;
"A CONDUCTIMETRIC DETECTOR WITH A WIDE DYNAMIC RANGE FOR LIQUID CHROMATOGRAPHY" Vratislav Svoboda et al., Journal of Chromatography, 148(1978), pp. 111-116 and 148(1978), pp. 111-116; and
"The Photo-Conductivity Detector--A New Selective Detector for HPLC" D. J. Popovich et al., Journal of Chromatographic Science, Vol. 17, 1979, Dec. pp. 643-650.
The devices for measuring the electric conductivity and the devices for measuring the absorbance based on the above-described literatures are separately marketed and used.
With increased uses of chromatography, various specimens are used and complicated specimens containing unknown constituents are increased, so that both a detecting device for measuring the electric conductivity and a detecting device for measuring the absorbance must be used simultaneously. In general, these devices are connected in series, so that a solution from a column first flows through a flow cell of the detecting device for measuring the electric conductivity and then flows through a flow cell of the detecting device for measuring the absorbance. The series-connected chromatographic process has the following serious disadvantages.
First, a solution flowing through a first flow cell causes turbulence, which produces further turbulence at the connection between the first and second flow cells. As a result, a chromatogram of specimen constituents dissolved from the column is distorted. The tubulence especially disturbs the measurement by the detecting device for measuring the absorbance. Especially in liquid chromatography, the quantity of a separated constituent of the specimen is determined by measuring the height or area of a peak of a chromatogram and the properties of the constituent are analyzed in response to a time required for dissolving the constituent. It follows, therefore, that the distortions of the peaks due to the distortion of the chromatogram cause great errors in measurement.
Secondly, conventional detecting devices for measuring the electric conductivity and absorbance have poor pressure resistance. Therefore, when use is made of a series connection of a detecting device for measuring the electric conductivity and a detecting device for measuring the absorbance, it is often likely that a solution leaks and that a detecting cell is broken. As a result, they unfit for use.
In order to solve the above described disadvantages there has been employed a method in which a solution derived from a column is divided by a divider or the like into two detectors. According to this method, the diffusion of the constituents of a specimen can be reduced, but turbulence occurs in the divider or the like so that the latter is clogged with dust entrained in the solution. Furthermore, a ratio of such a division varies due to a temperature variation, and accordingly the measurements with a good reproducibility are difficult.